countersink
     n 1: a hole (usually in wood) with the top part enlarged so that
          a screw or bolt will fit into it and lie below the
          surface
     2: a bit for enlarging the upper part of a hole [syn: {counterbore},
         {countersink bit}]
     v : insert (a nail or screw below the surface, as into a
         countersink) [syn: {set}]
     [also: {countersunk}, {countersank}]
Source: WordNet® 2.0